1. Field of the Invention
The invention relates to electrical apparatus, and more particularly, to circuit breakers having a releasable latch mechanism to provide shunt tripping operation.
2. Description of the Prior Art
Circuit breakers are widely used in industrial, commercial, and residential applications to provide protection for electrical apparatus and distribution circuits. Upon overcurrent conditions through a connected electrical circuit, the circuit breaker will automatically open to interrupt electric current flow through the circuit. Some circuit breakers utilize direct tripping operation wherein the circuit current flowing through the breaker also flows through a device such as a bimetal element or an electromagnet to directly actuate a latch mechanism. In multiple circuit breakers employing direct tripping operation, a separate trip mechanism is often employed for each pole. Overcurrent conditions through any pole of the circuit breaker will thus cause its associated trip device to function, effecting separation of the contacts of that pole. Since it is generally desirable to have all poles of the circuit breaker trip at the same time, such circuit breakers employ a trip bar or other means connecting the various poles of the circuit breaker to provide simultaneous tripping operation of all poles.
Other circuit breakers employ shunt tripping operation wherein a sensing device such as a current transformer is used to monitor the current flow through each pole of the circuit breaker and generate a tripping signal upon overcurrent conditions. Tripping signals from any pole can then in turn actuate a single latch mechanism to effect automatic separation of the contacts. A trip bar is also required on shunt tripping circuit breakers which employ multiple tripping modes, such as manual push-to-trip and undervoltage trip capabilities.
In order to provide isolation between the various poles of the circuit breaker, the trip bar must be insulated therefrom. Prior art circuit breakers have employed trip bars of molded insulating material which are rotated by the tripping action of any one pole or tripping device, thereby causing the other associated poles or tripping devices to also operate. A circuit breaker employing such a molded insulating rotating trip bar is described in U.S. Pat. No. 3,422,381 issued Jan. 14, 1969 to Julius Toth and assigned to the assignee of the present invention. Such an arrangement generally provides excellent service. However, under certain conditions problems can develop with rotating trip bars of molded insulating material, such as warping or breakage. It would therefore be desirable to provide a circuit breaker employing a metal trip bar.
Prior art circuit interrupters employing trip bars also lacked features which are advantageous for certain applications. For example, some circuit breakers in the prior art have required separate operations to reset the latch mechanism following a tripping operation. It would be desirable to provide a circuit breaker employing a self-resetting latch mechanism. It would also be desirable to provide a mechanism for releasing the latch of the circuit breaker without moving the trip bar.
In addition, for circuit breakers employing separate latch release mechanisms, trip mechanisms, and undervoltage trip mechanisms, it is desirable to provide means for automatically resetting all such mechanisms.